Wells are drilled into the Earth to allow recovery of hydrocarbons such as paraffins, napthenes, aromatics and asphaltics or gases such as methane. These wells may be vertical, deviated e.g. at an angle or horizontal depending on the size, location and nature of the reservoir into which they are drilled.
Once drilled, a series of liners and tubings may be installed such elements are sometimes known as completion. The gap between the wellbore and the completion is called the annulus. This can be filled with cement to prevent axial flow along the length of the well but can also be penetrated to allow fluid flow in some desired areas.
Open hole completions have no cement in the annulus but may still contain a tubular liner. This may have been installed where it was considered that the wellbore could collapse, but if that danger is not present then the well may be completed without any liner fitted. Such wells without completions are referred to as “barefoot”.
To aid recovery of hydrocarbon from the reservoir, a technique known as water flooding may be used. Additional wells are drilled and water is pumped into them under pressure. The water displaces oil from the formation and helps to maintain reservoir pressure. When injecting water in long horizontal wells, a method called linedrive can be used, whereby horizontal producer wells and water injector wells are drilled in alternating order.
The objective of the linedrive method is to inject water evenly from the entire length of the injection well. This should cause an even displacement of oil into the production wells so maximising the amount that is recovered from the reservoir. However, natural fractures or other conductive features are sometimes present in the formation which can cause water to travel preferentially or “short-circuit” from the water injector to the producer well. This results in a suboptimal displacement of the oil and reduces the total amount recovered from the formation. Within the industry, this is referred to as non-conformance and is illustrated in FIG. 1. The narrow arrows show the undesired short circuit route for water compared to the preferred water flooding effect which is shown with wide arrows placed along the water injection well with direction toward the production well.
In order to treat this type of non-conformance a first step is to determine where water enters the horizontal section of an oil production well unevenly. This may be achieved by a number of current methods such as production logging tools (PLT) which may be conveyed on coiled tubing, electric wireline or on jointed tubing. Wireline or possibly coiled tubing also requires a tractor to pull the PLT into the horizontal well. Use of a tractor introduces an additional problem in barefoot wells since existing tractors are not able to grip the formation or propel the tractor with sufficient force to overcome increasing friction of the wireline or tubing. Also, tractors may not have the required expansion ratio to be able to operate in uneven open holes. Having been deployed through small diameter upper tubing they may not be physically able to grip a wide hole.
Where deployment is considered possible, heavy equipment is also required which can often cause logistical problems at the well location, especially when operating offshore. It is also very costly. With very long horizontal wells it may also be impossible for these tools to reach the end of the well so the objective of this type of deployment will not be met. It is therefore advantageous to have a method to detect the water inflow into an oil production well without the need to use e.g. electric or memory logging tools.
Such an alternative is offered by the use of chemical tracers. Chemical tracers can be placed at various intervals on a completion in a producer well (positions 1, 2 and 3 in FIG. 1) and are dissolved into oil and/or water. The oil/water-flow then carries the tracer to the surface, where the tracer is detected. The presence of chemicals from known positions in the well can help determine which parts of the well are being affected by water and whether oil is flowing from all sections.
Tracer technologies are currently available in several forms.
US 2009/0087912 discloses a tagging system and a method comprising release of particles having a miniature body and configured to provide a non-radioactive resolvable optical emission in a distinguishable pattern when illuminated to a subsurface location. US 2009/0087912 comprises chambers (50, 52) containing particles (10), the compartments are carried by a downhole tool and are not stationary relative to the subterranean formation.
US 2001/036667 discloses a method for monitoring and detection according to which method the reservoir is divided into a number of zones/sections and specific tracers with unique characteristics for each zone/section are placed as integrated parts of the well completion. The tracers are chemically immobilized or integrated into the formation or in/on the constructions/filters around the wells. The tracers or tracer carriers are chemically intelligent and released as a function of specific events [0019]. It is suggested that a number of tracers (5) can be packed or immobilized into a small package (12), e.g. a chemically intelligent gel or a polymer package (11). It is not suggested in US 2001/036667 that the tracers can be held in or released from a canister.
WO2013/009895 discloses a method and system for reservoir interrogation where a tracer is encapsulated in a receptacle. The encapsulation is constituted by thin spherical shells normally made of a polymer which can turn permeable under certain conditions and release the chemical tracer held inside. It is not suggested in WO2013/009895 that the tracers can be held in or released from a canister.
US2011/0257887 discloses a method for monitoring a wellbore by providing a tracer material at one or more subterranean locations within or proximate the wellbore where the tracer may enter the flow and be present in the flow from the wellbore. The tracer may be supplied within a container being part of an apparatus placed in the wellbore at completion and released into the flow by operating that apparatus [0033]. There are no details in relation to the container and it is not suggested that a canister is driven into the wellbore. According to [0074] the tracer can be placed in a container (50) mounted on the exterior of the production tubing (14).
WO 2001/81914 discloses a method comprising dividing regions around wells in the reservoir into a number of sections, and injecting or placing specific tracers with unique characteristics for each section into the formation in these regions. The tracers are chemically immobilized/integrated in the formation or in constructions/filters around the wells, the tracers (tracer carriers) being chemically intelligent and released as a function of specific events. Detecting the tracers downstream provides information about the various zones.
WO 2007/102023 describes a similar concept with novel materials being used. It also describes a method of applying tracer material to a well via detonation. The proposal is that tracer material is introduced into the path of explosive energy from a perforation tool, which is known equipment within the industry. Detonation of the perforation charge shall then scatter the tracer in the well. This method applies the tracers as residue from an explosive detonation. A disadvantage is that there is uncertainty over the amount of tracer that will be applied to the wall of the wellbore. Detonation may also not completely transfer the tracer in its path.
Regardless of how chemical tracers may be applied to the wellbore, the current state of technology is that fluid samples must be collected from the wellhead and analysed at a remote laboratory. There is no immediate method of determining the presence of known tracer elements in fluids from the well. However, WO 2011/132040 describes the concept of detecting chemical tracers at the well head rather than by remote analysis.
The present specification discloses a novel method according to which different traceable components are attached at various positions along a barefoot well. The traceable components shall be installed and held in a dispenser such as a carrier or canister which dispenser shall be attached in the walls of the production well at desired intervals. The traceable components is then released gradually over time and carried to the surface by fluids from the production well.